Various products are furnished to the user or applicator in two parts which are to be mixed together in specified proportions prior to use. This is particularly true in the case of epoxy resins and adhesives which are furnished in a resin portion and a hardener portion, for example. In this case, the specified porportioned quantities of each are mixed together and they "set-up" or cure in a given period of time called the "pot-life" of the mixture. In other words, once the resin and hardener are mixed together, the user has an elapsing time period in which to use the mix before it sets up or cures. Unused material in the pot after the expiration of the pot-life period becomes unusable. While a small volume user can mix a pint of hardener with a quart of resin and do a one-time job before the pot-life period expires, the industrial user who continually uses such material cannot be constantly mixing small quantities to maintain his supply within the pot-life period. Also, the industrial user cannot mix 55 gallons of resin and 30 gallons of hardener to have a day's supply when he is not using an 85 gallon quantity within the pot-life period. A man applying epoxy on a production line needs a constant fresh supply in order to apply the material as desired.
The various proportional metering devices of the prior art have built in invariable proportional supply and thus the mix can't be changed without changing the apparatus structurally as is sometimes desirable with faster or slower production rates, various batches of material, and/or material which have different reaction time periods. Also the devices of the prior art, upon a malfunction or a stoppage in various supply lines, have no means of indicating to the user where the trouble has occurred. This involves shutting down the operation and exploring the entire metering device to find and correct the trouble. Also, the prior art apparatus does not have the means to seal off the system during periods of shut-down which is desirable to provide ready-to-go set up.